Downlink Control Information (DCI) is carried over a Physical Downlink Control Channel (PDCCH) to effectively transmit uplink or downlink scheduling information and related common control information. 10 DCI formats have been defined so far in the Long Term Evolution (LTE) system. Main functions of the respective DCI formats can be as depicted in Table 1. Moreover in a DCI channel encoding procedure, firstly a Cyclic Redundancy Check (CRC) is performed on and CRC information is added to DCI bits, and then the CRC information is scrambled by a Radio Network Temporary Identifier (RNTI), and next the DCI bits are channel-encoded, and the channel-encoded DCI bits are matched in rate.
TABLE 1DCIformatFunction0For scheduling of a Physical Uplink Shared Channel (PUSCH)1For scheduling of Physical Downlink Shared Channel (PDSCH)of a downlink single code word1AFor compact scheduling of a PDSCH of a downlink singlecode word1BFor compact scheduling of a PDSCH of a pre-coded downlinksingle code word1CFor a more compact scheduling of a PDSCH of a downlinksingle code word1DFor compact scheduling of a PDSCH of a downlink singlecode word with pre-coding and power offset information2For scheduling of a PDSCH of double code words inclosed-loop spatial multiplexing2AFor scheduling of a PDSCH of double code words in open-loopspatial multiplexing3Power control information for transmitting Physical UplinkControl Channels (PUCCHs) and PUSCHs of a group of users,where the power control information is indicated in 2 bits3APower control information for transmitting PUCCHs andPUSCHs of a group of users, where the power controlinformation is indicated in 1 bit
These DCI formats are further categorized into four categories dependent upon their functions: DCI formats for uplink PUSCH scheduling. e.g., the DCI format 0; DCI formats for downlink PDSCH scheduling, e.g., the DCI formats 1, 1A, 1B, 1D, 2 and 2A; DCI formats for scheduling common control information, e.g., the DCI formats 1A and 1C; and DCI formats for scheduling group-cast power control information, e.g., the DCI formats 3 and 3A.
The PDCCH is configured to carry DCI including scheduling information, uplink power control information, etc., for downlink and uplink data transmission. FIG. 1 illustrates a physical layer handling procedure of the PDCCH. The PDCCH is design by sharing a resource among a number of user equipments, a user equipment needs to search the entire control region of a downlink sub-frame for control signaling under some rule. In the DCI carried over the PDCCH, a Cell-Radio Network Temporary Identifier (C-RNTI) of the user equipment is scrambled onto a 16-bits CRC sequence to identify implicitly the destination user equipment to which the DCI is transmitted. In a downlink sub-frame, a number of pieces of DCI are encoded and rate-matched parallelly, and the encoded bits are multiplexed and then scrambled, modulated, interleaved, etc., together.
In order to support link adaptation and to low the complexity of detection by the user equipment as much as possible, mapping of PDCCH resources is designed per Control Channel Element (CCE), where a CCE is consisted of nine Resource Element Groups (REGs), i.e., 36 Resource Elements (REs). Furthermore a base station can select 1, 2, 4 or 8 CCEs to carry a piece of DCI dependent upon the length of carried DCI bits and a channel condition, where 1, 2, 4 or 8 is referred to as a CCE aggregation level, for example, 1 is referred to as a CCE aggregation level 1. The user equipment searches the control region for both the starting position of the CCEs where the DCI is located and the CCE aggregation level applied to the base station, and this procedure will be referred to PDCCH blind detection.
The set of CCE resources for which the user equipment performs PDCCH blind detection will be referred to as a PDCCH search space, where a common search space and a specific search space are defined in the standard. The common search space is shared by all the user equipments in a cell, and starts from the first CCE in a sub-frame. The user equipment needs to be attempt on the CCE aggregation levels 4 and 8 in the common search space. The specific search space specific to each user equipment involves all the possible CCE aggregation levels. At a CCE aggregation level, the starting position of the specific search space of the user equipment is determined jointly by the sub-frame number, the RNTI of the user equipment, etc., and FIG. 2 illustrates a schematic diagram of PDCCH blind detection. Additionally the number of candidate PDCCH positions for which the user equipments needs to perform blind detection is further defined in the standard as depicted in Table 2. For each of the candidate PDCCH position, the user equipment needs to attempt on decoding DCI of two different types of lengths, so the user equipment needs to perform a total number 44 of times of blind detection in a downlink sub-frame.
TABLE 2Number ofCandidatetimes ofCandidate CCEPDCCHblindType of search spaceaggregation levelpositiondetectionSpecific search space16122612424824Common search space448824TotalN/A (Not Available)2244
In a Time Division Duplex (TDD) system, the same frequency resources are applied to uplink and downlink transmission, and an uplink or downlink signal is transmitted in different time slots. FIG. 3 illustrates a frame structure in the LTE TDD system, where seven uplink-downlink configurations as depicted in Table 3 are supported in an uplink-downlink sub-frame allocation scheme.
TABLE 3Uplink-Downlink-downlinkto-Uplinkconfigu-Switch-pointSub-frame numberrationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
As the technologies are developing rapidly, an increasing number of small cells, home eNBs and other low-power eNBs have been deployed for local coverage, and cells covered by the low-power eNBs will be referred to small cells. There are a smaller number of user equipments with a significantly varying service demand in the small cells, so there will be such a situation that an uplink-downlink service proportion required of the small cells may vary dynamically. In view of this, the base station needs to indicate the TDD uplink-downlink configuration information frequently to the user equipment, but a solution to indicating the TDD uplink-downlink configuration information to the user equipment has been absent in the prior art.